1. Field of the Invention
The present invention relates generally to self-cleaning screen assemblies for use in shallow water pumping systems. In particular, the present invention relates to a check valve assembly for use with a self-cleaning screen in a shallow water pumping system to maintain a prime in a centrifugal pump.
2. Description of the Related Art
Centrifugal pumps are commonly used to suck water out of outdoor pits, reservoirs, streams, rivers, ponds, and the like, especially for irrigation purposes. A suction pipe or hose typically extends between the water source and the centrifugal pump for supplying water to the pump. A screen is typically used to prevent debris, sand and other objects from being sucked into the suction pipe or hose and into the pump while pumping.
Self-cleaning screens have been developed to prevent plugging by debris being drawn to the screen during pumping. An example of a self-cleaning screen is provided in U.S. Pat. No. 6,270,669 issued to Bauer. Another example of a self-cleaning screen is an earlier version of the product marketed by the Applicant under the proprietary name RIVERSCREEN™. These known products provide rotary self-cleaning drum strainers having a means for cleaning debris from a drum as the drum rotates during operation of the pump. The filtered Water passing into the drum is sucked from the interior of the drum by a suction pipe or hose for delivery to a centrifugal pump.
A well-known limitation to the use of centrifugal pumps is their limited ability to draw fluid for self-priming when starting from an air-filled or dry condition. The impeller is typically not capable of generating a sufficient vacuum when operating in air to draw liquid up to the pump when the standing level of the liquid is below the pump. Before liquid reaches the impeller, very little draw is generated by the impeller. Thus, to begin pumping, the pump must either be primed manually or be self-priming.
Self-priming centrifugal pumps are well known. Examples of such pumps are disclosed in U.S. Pat. Nos. 6,409,478 and 6,783,330 issued to Carnes et al. Although self-priming centrifugal pumps have been used effectively under some conditions, they have generally suffered from a relatively greater complexity, higher expense, unreliability, and/or an inability to lift water as high as necessary to prime the pump in some applications.
There is a need in the industry for an improved self-cleaning screen for use with a centrifugal pump to filter the water entering the pump and to maintain a prime in the pump.